Method for making wood and plastic composite material

ABSTRACT

A method of preparing wood and plastic to produce a composite material.

RELATED APPLCIATIONS

This is a divisional application of co-pending U.S. patent applicationSerial No. 09/558,895, entitled “Wood and Plastic Composite Material andMethods for Making Same,” filed Apr. 26, 2000, the entire disclosure ofwhich is incorporated herein by reference.

GOVERNMENT RIGHTS

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Grant98-G-3138 awarded by the U.S.D.A., U.S. Forest Service.

BACKGROUND OF THE INVENTION Field of the Invention (Technical Field)

The present invention relates to a method of preparing wood and plasticto produce a composite material.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

The present invention comprises a method of preparing natural materialparticles for making a composite material. According to a preferredembodiment the method comprises the steps of logging natural material;grinding logged natural material; screening ground natural material; andgrinding screened natural material. In a preferred embodiment, the firstgrinding step comprises grinding the natural material to a maximumparticle dimension of less than approximately 12 inches. In a preferredembodiment, the method further comprises a washing step before thesecond grinding step and/or a drying step before the second grindingstep. According to a preferred embodiment, the second grinding stepcomprises grinding the natural material to a maximum particle size ofless than approximately 0.5 inches. In a preferred embodiment, themethod further comprises a chunking step before the first grinding step,a screening step additionally comprising a washing step, a flaking stepbefore the second grinding step, and/or a sifting step after the secondgrinding step. A sifting step is useful for, but not limited to,producing material comprising a more uniform size.

The present invention also comprises a press method of making acomposite material. In a preferred embodiment, the method comprises thesteps of: providing a frame; loading natural material and plastic intothe frame; and applying heat and pressure to the natural material andplastic in the frame. According to a preferred embodiment, the methodfurther comprises a step of removing the composite material from theframe after the applying step, a step of inserting a forming box intothe frame, and/or a step of adjusting the packing of the naturalmaterial and plastic before the applying step.

In a preferred embodiment, the applying step comprises applying heat toreach a temperature of at least approximately 300° F. and/or theapplying step comprises applying a pressure of at least approximately 4psig. In a preferred embodiment, the applying step comprises applyingheat to reach a temperature of approximately 400° F. and/or the applyingstep comprises applying a pressure of approximately 8 psig.

The present invention also comprises an extrusion method of makingcomposite material. According to a preferred embodiment, the methodcomprises the steps of: feeding natural material and plastic into anextruder; heating the natural material and plastic in the extruder; andextruding composite material comprising the natural material and plasticfrom the extruder. In a preferred embodiment, the extruding stepcomprises extruding composite material onto a film. In another preferredembodiment, the method further comprises a step of rolling extrudedcomposite material between two rollers and/or a step of cooling extrudedmaterial.

The present invention also comprises a method of making compositematerial comprising the steps of: processing natural material; andmaking composite material comprising natural material and plasticwherein making comprises at least one method selected from the groupconsisting of press methods and extrusion methods.

A primary object of the present invention is to produce a wood andplastic composite material.

A primary advantage of the present invention is economy of preparationof wood and plastic raw materials and production of a composite materialcomprising the same.

Other objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate several embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating a preferred embodiment of the invention and are not to beconstrued as limiting the invention. In the drawings:

FIG. 1a is a scanned image measuring 3 inches by 3 inches of a crosssection of a preferred embodiment of a composite board of the presentinvention;

FIG. 1b is a scanned image measuring 3 inches by 3 inches of a crosssection of a preferred embodiment of a composite board of the presentinvention;

FIG. 2 is a drawing of a press apparatus for a preferred embodiment ofthe press method of the present invention;

FIG. 3 is a drawing of an extrusion apparatus for a preferred embodimentof the extrusion method of the present invention;

FIG. 4 is a drawing of a production process for a preferred embodimentof the present invention.

FIG. 5 is a plot of retained material versus sieve size for a wood andplastic blend of a preferred embodiment of the present invention;

FIG. 6 is a plot of retained material versus sieve size for a wood andplastic blend of a preferred embodiment of the present invention;

FIG. 7 is a plot of retained material versus sieve size for a wood andplastic blend of a preferred embodiment of the present invention;

FIG. 8 is a plot of retained material versus sieve size for a wood andplastic blend of a preferred embodiment of the present invention;

FIG. 9 is a plot of retained material versus sieve size for a wood andplastic blend of a preferred embodiment of the present invention;

FIG. 10 is a plot of retained material versus sieve size for a wood andplastic blend of a preferred embodiment of the present invention;

FIG. 11 is a graph of bending strength comparing various materials;

FIG. 12 is a graph of bending stiffness comparing various materials;

FIG. 13 is a graph of internal bond strength comparing variousmaterials;

FIG. 14 is a graph of nail withdrawal strength comparing variousmaterials;

FIG. 15 is a graph of edgewise shear comparing various materials;

FIG. 16 is a graph of water absorption comparing various materials;

FIG. 17 is a graph of thickness swell comparing various materials; and

FIG. 18 is a graph of linear expansion comparing various materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS BEST MODES FOR CARRYING OUT THEINVENTION

The present invention comprises a composite board and a method of makingthe same. Practice of particular preferred embodiments of the presentinvention enhances recovery of the grasslands and watershed of theSouthwest United States when a scrub tree (such as a one-seeded juniper)is mixed with plastic and processed to create a quality product, e.g.,water-resistant and rot-proof. In panel form, such high quality productare suitable for sign manufacturing, housing construction, marineconstruction and other purposes. The present invention also comprisesother trees, such as, but not limited to, ponderosa pine.

Composite Material

The present invention comprises a composite material and a method ofmaking the same. In general, the composite material of the presentinvention comprises natural material, for example, wood, and plastic.Wood includes, but is not limited to hard and soft wood trees such asApache Plume; Ash, single-leaf; Bitterbrush; Cliffrose; Fendlerbush;Juniper, one-seed; Juniper, Rocky Mountain; Mahogany, curl-leaf;Mahogany, mountain; Mockorange; Ponderosa Pine and Mormon Tea. Accordingto the present invention, natural material comprises wood including forexample, material from a tree, not limited to, leaf material, branchmaterial, trunk material, bark material, needle material and rootmaterial. Composite material comprising particles of such materials arepreferred. Plastic includes, but is not limited to, polypropylene,polyethylene, and the like. According to a preferred embodiment,composite material of the present invention comprises at least 20%juniper wood and at least 20% plastic. Optional additives includecolorants, UV protectorants, flame and fire resistants, and the like.

Composite material of the present invention is manufactured via eitherpress or extrusion methods. Wood ingredients are passed through a millto achieve a desired particle size. Plastic is provided in a formsuitable for mixing with the wood, for example, but not limited to, inthe form of a fluid, pellets, flakes, granules, or powder as known inthe art. In a preferred embodiment, composite material is

Method of Making Composite Material

Composite material of the present invention is manufactured via eitherpress or extrusion methods. Wood ingredients are passed through a millto achieve a desired particle size. Plastic is provided in a formsuitable for mixing with the wood, for example, but not limited to, inthe form of a fluid, pellets, flakes, or powder. In a preferredembodiment, composite material is manufactured comprising panelgeometry, for example, but not limited to, panel geometry used inconstruction of buildings. In another preferred embodiment, compositematerial is manufactured comprising beam and/or post geometry, forexample, but not limited to, beam and/or post geometry used inconstruction of buildings. Manufacture of such composite materials withsuch geometry is achieved through press and/or extrusion techniques. Itis to be understood by one of ordinary skill in the art that the term“board” is used in a non-limiting sense. Therefore, the term “board” asused throughout this disclosure comprises panel and other geometry thatare achieved through the press and extrusion methods disclosed within. Adiscussion of inventive press methods and inventive extrusion methodsfollows. Thereafter, inventive methods of wood preparation arediscussed.

Press Method

Press methods of the present invention rely on at least one press.Pneumatic, mechanical and/or hydraulic presses are suitable for thepress method of the present invention. The inventive press methods ofthe present invention process wood/plastic mixtures into, for example,composite board.

A press apparatus 20 of a preferred embodiment of the present inventionis shown in FIG. 2. This press comprises an upper platen 22 and a lowerplaten 24. The lower platen 24 is driven upward by a drive mechanism 26.Of course, a press comprising a moveable upper platen is also within thescope of the present invention. As shown in FIG. 2, a composite materialassembly 28 is positioned between the upper platen 22 and the lowerplaten 24. The composite material assembly comprises a lower plate,called a caul plate, 30, a frame 32, a composite mat 34 and an uppercaul plate 36. According to the present invention, at least one of theplatens is heated to a temperature sufficient to melt the plasticcomponent of the composite material. Heating of the at least one platenoccurs optionally before or after engagement of the drive mechanism 26.In a preferred embodiment of the present invention, both platens areheated prior to application of pressure to the composite mat 34. In thispreferred embodiment, the drive mechanism 26 drives the lower platen 24upwards until the upper platen 22 contacts the upper caul plate 36 andcompresses the composite mat 34. The plastic component of the compositematerial mat 34 melts due to heat transferred to the mat 34 from theheated platens

Of course the rigidity of the final product depends on a variety offactors including thickness, type of plastic, ratio of wood to plastic,amount of gas entrained, pressure of entrained gas, whether an enforcingmesh, rods, bars or other enforcing material is incorporated into themat or slurry. Rigidity is also controllable through use of exteriorfilms. Exterior films such as, but not limited to, reflective and/orcolored films are also useable and may optionally add rigidity to afinal product. Films are optionally added before, during, or afterapplication of pressure and/or heat.

As described above, the press method of the present invention optionallyuses a frame having an appropriate thickness. This frame contains thewood/plastic material as it is heated and/or compressed. Therefore, theframe must withstand the temperatures and/or pressures associated withthe press method. In a preferred embodiment, the frame is constructedfrom a piece of metal, for example, a single piece of metal from which acenter section is cut and removed. The remaining frame comprises anydesired configuration, including, but not limited to, rectangular,round, arbitrary and configurations typically used by federal and stateagencies for signs. In a preferred embodiment, the amount of compositematerial placed into the frame to form the mat and subsequently, theslurry, is calculated as to prevent overflow of material. Overflowoccurs when the volume of the slurry exceeds that of the frame cut-out.

In a preferred embodiment, a “forming box” (a forming box is used to“form” or “lay up” the mat of wood and plastic) is placed inside theframe. The forming box is optionally marked with graduations such as anapproximately 1 inch border and a red line every approximately half inchand a black line every approximately ¼ inch. The forming box allows forloading of the frame minimizing risk of composite material spilling overthe edge of the frame. In general, before heating and/or compression,the composite material is less dense and therefore occupies a greatervolume. Thus, a manner of containing the composite material duringloading is helpful. A forming box comprising graduations allows for moreaccurate leveling of the composite material across the breadth of theframe.

In an alternative embodiment, a forming box comprising an adjustable lidis useful for practicing the press method of the present invention. Insuch an embodiment, the lid is adjusted to a predetermined height andwood/plastic composite material is introduced into the volume created bythe press, the frame and the lid. Material is preferably introducedthrough at least one opening in the lid. In such processes,substantially uniform distribution of the wood/plastic material ispreferred to ensure final product quality.

Of course, devices that assist in placing composite material within theframe are within the scope of the present invention. Such devices mustaccount for the “powder-like” characteristics of the composite materialthat exists before heating. Techniques and equipment known in the art ofpowder handling are suitable for use with the present invention inloading the frame. Caution is required in the loading step, however, toavoid segregation of the wood and plastic. Techniques known in the artof powder handling include, but are not limited to, air transport,mechanical transport, and electromagnetic transport. For example, anaeromechanical conveyor is manufactured by Angus Powderflight Limited,Derbyshire, England UK. This aeromechanical conveyor is a powdertransporting device consisting of a constant diameter tube containing aseries of discs mounted at fixed intervals on a cable, and with a drivemechanism that can propel the discs through the tube at a velocitysufficient to cause turbulence within the powder and surrounding air.Additionally, no separation occurs when transferring powder blends, evenwhere there are considerable variations in density and particle size.However, it is advisable to monitor metering when using such a system.Spiral conveyors are another example of conveyors that are suitable forloading the frame. Again, prevention of wood and plastic segregation isimportant to forming a high quality composite board.

In embodiments where loading does not also achieve leveling, anadditional leveling step is helpful. Leveling is achievable through useof a trowel, screed or the like.

In instances where loading and/or leveling do not achieve asubstantially uniform packing/density, a pre-press compression step isoptionally helpful. Pre-press compression of the wood/plastic materialis achievable through use of a board or boards that are placed onto theloaded and leveled wood/plastic material. When a suitablepacking/density is achieved, according to the press method of thepresent invention, the wood/plastic material is referred to as a mat.Next, the mat must be prepared for application of heat and/or pressure.

In embodiments comprising a forming box, the mat must first be preparedsuch that removal of the forming box does not substantially disturb themat. To achieve this goal, a cover is used comprising a breadth smallerthan that of the forming box. This cover is placed on top of the mat toensure integrity of the mat edges during forming box removal. In analternative embodiment, only corners of the mat are protected. Forexample, square and/or L-shaped plates are placed over the corners ofthe mat to ensure the mat's integrity while the forming box is removed.In another embodiment, the forming box comprises compression meanswhereby the sides of the forming box compress and then release such thata gap is created between the mat and the forming box. The presence of agap helps to ensure mat integrity during removal of the forming box.After forming box removal, the additional frame, and/or frame-likeelements, are removed from the mat. In an alternative embodiment, aplate that covers the entire mat is placed on top of the mat. In such anembodiment, the plate is not removed after removal of the forming box.In embodiments that do not comprise a plate as an additional frame, orthe like, a plate is placed on top of the mat. This plate comprisesphysical properties sufficient to withstand the heat and/or pressure ofthe press.

Next, the press is heated to a temperature sufficient to melt theplastic. Once this temperature is reached, the press is engaged suchthat the press and the plate compress and/or heat the wood/plasticmaterial. In a preferred embodiment, the press is heated to atemperature greater than approximately 300° F., and preferablyapproximately 360° F. or greater, and a pressure of greater thanapproximately 200 pounds per square inch is applied. In the press methodof the present invention, the press is applied for a period of time. Ina preferred embodiment, the press is applied for approximately 30minutes. The heat and/or pressure are then decreased. Optionally,depending on the selected temperature schedule, a decrease may occurprior to expiration of the press application period. A decrease intemperature is referred to as cooling. In a preferred embodiment of thepresent invention, cooling occurs after an approximately 30 minuteheating period. After cooling, the composite board is removed from thepress.

In a preferred embodiment of the present invention, the press methodcomprises the following steps: providing a frame, loading thewood/plastic material into the frame, applying heat and/or pressure tothe material in the frame, and removing the composite board from theframe. In alternative embodiments, the press method optionally comprisesthe steps of inserting a forming box into the frame, placing the frameon the bottom caul plate, leveling the wood/plastic material in theframe, adjusting the packing/density of the wood/plastic material in theframe, forming a wood/plastic material mat in the frame, protectingedges and/or corners of the mat, removing the forming box from theframe, and/or placing a caul plate on top of the mat.

In another preferred embodiment of the present invention, heatingcomprises use of electromagnetic radiation, preferably of a frequencysuch that absorption of the radiation is maximized. In yet anotherpreferred embodiment of the present invention, heating comprisesinduction heating.

EXAMPLE

Wood and plastic were mixed and placed in a frame positioned on a largeformat press. Heaters were used to reach a temperature of approximately400° F. and airflow of the press was set to approximately 650 scfm witha plenum pressure of approximately 8 psig. The wood and plastic materialwas heated and compressed using the press. After cooling, the compositeboard formed through this press process was removed from the press.

Extrusion Method

Extrusion methods rely on a mechanical device known as an extruder. Ingeneral, an extruder has an inlet for receiving raw materials and anoutlet for processed material. Extruders often comprise a screw forconveying material from the inlet to the outlet. Some extruders comprisemore than one screw, for example, a twin-screw extruder.

The extrusion method of the present invention relies on at least oneconventional extruder. A preferred embodiment of an extrusion method ofthe present invention is shown in FIG. 3. The method shown in FIG. 3comprises an extrusion method apparatus 40. At a fore end of theextrusion apparatus is an extruder 42. The extruder 42 comprises aninlet 44 for feeding material and an outlet 46 for outputting extrudedmaterial. As known in the art of extrusion, the extruder is optionallyheated or cooled at points, and/or zones, along the extruder, includingthe inlet and/or outlet. As shown in FIG. 3, the outlet 46 comprises aheader comprising a plurality of sub-outlets. Alternatively, an outletof the extrusion method of the present invention comprises at least onemoving outlet that moves substantially horizontally over time. In eitherinstance, the outlet, and/or sub-outlets, deposit outputted extrudedmaterial onto a surface.

In the particular embodiment shown in FIG. 3, a rolling film 52 that isstored on a film roller 50 provides a surface. Furthermore, in thisparticular embodiment, an upper rolling film 52 is used in conjunctionwith a lower rolling film 52′ that is stored on a film roller 50′. It isunderstood, however, that the upper film is optional to the extrusionmethod of the present invention. Additionally, provision of a filmsurface is not limited to, for example, film stored on a roller. Film,and/or an alternative surface providing material, may come from a stack,a suitable fluid, a metal surface, an extruder and the like. Forexample, a layer of air having sufficient pressure is suitable forproviding a “surface” onto which extruded material may be deposited, asis a layer of water. Regarding an extruder as providing a surface, thoseof ordinary skill in the art are familiar with co-extrusion methodswherein the same or an additional extruder is used to form a film thatis optionally co-extensive with a core extrudate. For example, anextruder head that provides for at least one film while also providingfor a core extrudate is within the scope of the present invention. Whena film is extruded, it is known in the art to use a layer of air havingsufficient pressure to support and/or cool the extruded film. When suchan extrusion method apparatus of the present invention comprisesextruded film, that film is optionally colored and/or mixed with otheradditives. In a preferred embodiment of the present invention, at leastone side of the extruded composite material is coated with a filmcomprising a reflective material and/or a colored material.Alternatively, a reflective and/or colored material is added to thecomposite material before, during and/or after extrusion.

Once the extruded material, as shown in FIG. 3, has been deposited ontothe rolling film 52, the deposited material and rolling film istransported to a roller drum 60. In this embodiment, the extrusionmethod apparatus comprises a lower roller drum 60′ and an upper rollerdrum 60. In general, when two roller drums are used, at least one drumis positionable to adjust the gap between the two drums. In analternative embodiment, only a single roller is used whereas in anotheralternative embodiment, a suitable surface is used for receiving filmclad composite extrudate, a suitable surface comprises both lowfriction, “sliding” surfaces and high friction, “traction” surfaces.High friction, traction surfaces optionally comprise treads, spikesand/or barbs and the like for increasing friction and/or impartingsurface indicia and/or holes. The extrusion method apparatus shown inFIG. 3 optionally applies force to at least one of the roller drums toevenly disperse and/or control the thickness and/or width of theextrudate. The roller drums of the extrusion method apparatus are alsooptionally temperature controlled for heating and/or cooling theextrudate and/or film, for example, one side may be heated while theother is cooled, both sides may be heated or cooled, or heating and/orcooling may occur periodically.

As shown in FIG. 3, at a distal end of the extrusion method apparatus40, is a cooling unit 70. The cooling unit removes energy from theextrudate and/or film. In an alternative embodiment, comprising coolingrollers, a cooling unit is not necessary or can be used in conjunctionwith heating/cooling roller.

The extrusion method of the present invention is flexible in thatcomposites are manufacturable in a variety of geometries. It isunderstood by one of ordinary skill in the art of extrusion that theextruder outlet 46 and other components are configurable to manufacturea variety of geometries. Furthermore, the extrusion method is optionallyapplicable to filing of molds.

In a preferred embodiment of the present invention, the extrusion methodcomprises the following steps: feeding composite material into anextruder, heating the composite material, and extruding the compositematerial from the extruder. In alternative embodiments, the extrusionmethod optionally comprises extruding composite material onto a film,rolling extruded material between two rollers, and/or cooling extrudedmaterial in a cooling unit.

EXAMPLE

An extruder was used to fill molds with the inventive composite. ASterling single screw extruder (Sterling/APV Chemical Machinery, NewJersey) with a two inch screw diameter was used to extrude the inventivecomposite. The approximately 4 foot long extruder was operated with anelectric motor having approximately 20 horsepower. A variable speed feedauger was used in conjunction with material vibrators to feed compositematerial into the extruder. Heaters were used to maintain a temperatureof approximately 520° F. The extruder was operated at a rate ofapproximately three cubic feet per hour. The extruder was outfitted withcontrollers for controlling the aforementioned variables. Of course, theselection of extruder operating temperature and rate depends onmanufacturing criteria related to, for example, economics and compositeproduct geometry. The extruder was used to manufacture composite beamscomprising dimensions of approximately 4 inches by 4 inches andapproximately 10 feet in length.

Wood Preparation Methods

In general, a process for making composite material of the presentinvention comprises several steps. These steps produce a wood materialthat is suitable for use in the aforementioned press and extrusionmethods of the present invention. The inventive wood preparation methodsthat follow, optionally alleviate problems such as volatiles andmoisture in the wood which can complicate, for example, extrusionprocessing.

In a preferred embodiment, the wood preparation method comprises fourmain steps: logging, grinding, screening and/or washing, and grinding.This preferred embodiment optionally comprises drying. According to thispreferred embodiment, whole trees are logged. Whole trees comprise forinstance, but are not limited to, one-seed Juniper and Ponderosa Pineand preferably comprise the aboveground portion of a tree and optionallycomprise roots. Logging is performed, for example, with a tractorcomprising a shear mechanism. Next, logged whole trees are ground to amaximum wood particle dimension of less than approximately 12 inches.Grinding is performed, for example, with a hog grinder, preferably to amaximum wood particle dimension of less than approximately 6 inches, andmore preferably to a maximum wood particle dimension of betweenapproximately 3 inches and approximately 5 inches. Next, the ground woodis screened and/or washed to remove debris, such as, but not limited to,dirt and sand. Depending on subsequent processing conditions, sand ispotentially detrimental due to temperature and/or pressure related phasetransitions to a liquid glass state. Screening and/or washing isperformed, for example, with a device comprising a rotating screen drumand optionally at least one spray nozzle for spraying fluid, forexample, gas and/or liquid. Next, the screened and/or washed ground woodis optionally dried. Drying is performed, for example, through use of arotating drum dryer and forced air or alternatively through naturaldrying processes such as sun and/or air facilitated drying. The dryingstep comprises reducing moisture content of the ground, screen and/orwashed wood to a moisture content of less than approximately 15% byweight, preferably to a moisture content of less than approximately 10%by weight and more preferably to a moisture content of less thanapproximately 5% by weight. Next, the wood is flaked or chipped to amaximum particle size less than approximately 0.5 inches, preferably toa particle size less than 0.25 inches and more preferably to a particlesize less than approximately 0.05 inches.

The method of the invention involves two grinding steps, a firstgrinding step and a second grinding step. Unless otherwise specified,and as further explained herein, the first “grinding” step means thereduction of chunked trees to pieces comprising dimensions less thanapproximately 5 inches and preferably to less than approximately 3inches. Thus, the first “grinding” does not reduce the material topowder; the second “grinding” step reduces the tree material to a muchmore powder-like consistency.

In another preferred embodiment, the inventive wood preparation methodof the present invention comprises eight steps. A first step compriseslogging in the field. Logging comprises removal of trees from theirearthen base, which typically comprises substantially removing treesfrom their root systems.

A second step comprising chunking takes place in the field or optionallyin a facility that is also designed for subsequent processing, i.e., aprocessing facility. A purpose of the chunking step is to reduce thesize of the tree for facilitating transport to a grinder, such as, butnot limited to, a hog grinder. Chunked trees are, under certainconditions, susceptible to degradation; therefore, time and storageconditions of chunked trees are factors that are useful in determiningwhether to perform chunking in the field or in a processing facility.

A third step comprising grinding is performed either in the field or ina processing facility. Grinding is performed using a grinder, such as,but not limited to, a hog grinder. Ground trees are, under certainconditions, susceptible to degradation; therefore, time and storageconditions of ground trees are factors that are useful in determiningwhether to perform grinding in the field or grinding in a processingfacility. When trees are ground in the field, they are optionallytransported to a processing facility, for example, via motorizedvehicles and/or conveyors. For example, ground wood is optionally loadedinto gaylords for delivery to a processing facility. Once at theprocessing facility, the gaylords are positionable on a hog grinderloader, which delivers material to the hog grinder. In a preferredembodiment of the present invention, a hog grinder is used to reducechunked trees to pieces comprising dimensions less than approximately 5inches and preferably to less than approximately 3 inches, morepreferably to approximately ¾ inch by approximately ¾ inch byapproximately 3 inch. The ground tree pieces are herein referred to as“chips.”

A fourth step comprising washing and/or screening of chips is performedin a processing facility. In a preferred embodiment of the presentinvention, a hog grinder drops chips onto a conveyor for transport to achip washer and screener. Purposes of washing and/or screening are towash chips and to remove any debris, such as, but not limited to, sand,dirt, rocks and other foreign material from the chips. Of course,washing conditions and screening conditions are selected to facilitatefurther processing and to enhance the quality of the final product. Forexample, additives known to effect wood are optionally added to thewashing solution, such additives include, but are not limited to, acids,bases, enzymes (e.g., cellulosic enzymes), gas concentrations and thelike. Environmental conditions of the washing solution are alsoadjustable to promote overall efficiency. Such conditions includetemperature and pressure. It is understood that the effect of additivesand environmental conditions can be cumulative and/or synergistic andoperate through physical and/or chemical principles. Furthermore,washing optionally comprises washing with a gas. Such an embodimentoptionally comprises gas delivered at a pressure sufficient to removedebris.

A fifth step comprising flaking of washed and/or screened chips isperformed in a processing facility. A purpose of flaking is to reducethe size of tree particles to a desired size. In a preferred embodiment,the desired particle size is less than approximately 2 inches, and morepreferably to less than approximately 0.5 inch. Flaked tree particlesare herein referred to as flakes.

A sixth step comprising drying of flakes is performed in a processingfacility. A purpose of drying of flakes is to reduce flake moisturecontent. In a preferred embodiment, moisture content is reduced toapproximately less than 20%, preferably to less than approximately 15%,and more preferably to less than approximately 10%. Drying is achievableby a variety of means, including, but not limited to, convection dryingand solar drying. In a preferred embodiment, a gas fired rotary dryer isused. This rotary dryer is inclined by approximately 20 degrees, therebydefining a “high” end and a “low” end. This rotary dryer is alsooperable in a continuous manner. In this rotary dryer embodiment, flakesare fed into the high end and flakes emerge from the low end. In analternative embodiment, a plurality of dryers are used wherein energysupplied to each dryer (e.g., energy for heat and/or rotation) arecontrollable and selected to achieve desirable end results, e.g.,reduced drying time, reduced energy input, and/or higher productquality.

A seventh step comprising finish grinding is performed in a processingfacility. A purpose of finish grinding is to reduce dried flakes to adesired size. In a preferred embodiment of the present invention, thedesired size comprises a particle size less than approximately 0.25 inchand more preferably a particle size less than or equal to approximately0.03125 inch.

An eighth step comprising sifting is performed in a processing facility.A purpose of sifting is to remove particles, or fines, from theprocessed material. The collected fines are useable as a facing materialor fuel, or alternatively, discarded as waste. In a preferredembodiment, material exiting the sifting step is transported by a gas,such as, but not limited to, air and gases that reduce the potential forcombustion. Transported material is immediately available for furtherprocessing or for storage.

Integration of Wood Preparation and Press and/or Extrusion Methods

According to the present invention, the wood preparation methods andpress and/or extrusion methods are combinable in a production process toproduce an inventive composite product. A preferred embodiment of aproduction process is shown in FIG. 4. As shown in FIG. 4, a woodreceiver 160 is used for receiving wood. Next, the wood is transportedto a screen 164 for screening out undesirable larger pieces of wood.Once screened, the wood is transported to a reducer 166 for reducing thesize of the screened wood. The reduced wood is transported to a washerand/or screener 168 that optionally comprises a re-chipper 170 forfurther reduction of screened wood. Next, the washed wood is flakedusing a flaker 172. From the flaker 172, the wood is transported to aflake receiver 176 that optionally comprises a heater and/or dryerand/or a dust burner 174. Flakes are then transported to a grinder 178for grinding and/or sizing of the wood. The ground wood is thentransported to a sifter 180 for sifting fines from larger pieces ofwood. Fines are transported to and stored in a fines receiver 186 whilethe larger pieces are transported to and stored in a processed woodreceiver 182. The fines receiver and processed wood receiver optionallycomprises filters 184, 188. The processed wood and/or fines are thenready for further processing and/or combination with plastic.

Plastic enters the production process through a plastic receiver 200.The plastic in the plastic loader is optionally transported to a plasticstorage receiver 196 for storage and/or further processing. The plasticstorage receiver 196 optionally comprises a filter 198.

Once the wood has been processed and/or stored, it is then transportedto a measurement system 190, for example, a weigh station system and/orflow measurement system. Once the plastic has been processed and/orstored, it is then transported to a measurement system 194, for example,a weigh station system and/or flow measurement system. The plastic andwood are transported to a blender 192 for blending plastic and wood.Blended plastic and wood are transported to a production line 202 thatcomprises a press and/or an extruder. The production line produces afinal product or optionally comprises additional equipment forperforming additional steps for producing a final product. For example,the production line optionally comprises an unloader and/or cooler 204;a trimmer and/or borer 206; an additional trimmer and/or borer 208; atransfer and/or inspection unit 210; a sander 212; an additionaltransfer unit and/or inspection unit 214; a paint unit 216, for example,for spray painting; an oven 218, for example, for curing paint and/orother material; a grade station 220; and/or a stacker 222, for stackingproduct. Product output from the production line is output generally ata product or stacked product output 224.

Example 1

A one layer composite panel, or board, of the present invention wasmanufactured. The panel comprised approximately 50% by weight of juniperand approximately 50% by weight of polypropylene. The juniper wasprocessed with a hammermill to approximately {fraction (1/32)} inch anddried to a moisture content of less than 1%. The panel comprised thefollowing target characteristics: length of approximately 46 inches;width of approximately 46 inches; thickness of approximately 0.625inches; specific gravity of approximately 0.95 and a total mass of20,592 grams. A press temperature of approximately 195° C. was usedtogether with a press time of approximately 30 minutes and a maximumgauge pressure of approximately 900 psi. A cooling time of approximately15 minutes was used. The final panel had a mass of approximately 20,440grams, a thickness of approximately 0.615 inches, and a specific gravityof approximately 0.96. Thus, the actual characteristics for specificgravity and thickness were within approximately 2% of the targetcharacteristics.

Example 2

A one layer composite panel, or board, of the present invention wasmanufactured. The panel comprised approximately 50% by weight of Juniperand approximately 50% by weight of polypropylene. The juniper wasprocessed with a hammermill to approximately ¼ inch and dried to amoisture content of less than 1%. The panel comprised the followingtarget characteristics: length of approximately 46 inches; width ofapproximately 46 inches; thickness of approximately 0.625 inches;specific gravity of approximately 0.95 and a total mass of 20,592 grams.A press temperature of approximately 195° C. was used together with apress time of approximately 30 minutes and a maximum gauge pressure ofapproximately 900 psi. A cooling time of approximately 15 minutes wasused. The final panel had a mass of approximately 20,525 grams, athickness of approximately 0.665 inches, and a specific gravity ofapproximately 0.89. Thus, the actual characteristics for specificgravity and thickness were within approximately 7% of the targetcharacteristics.

Example 3

A one layer composite panel, or board, of the present invention wasmanufactured. The panel comprised approximately 50% by weight of Juniperand approximately 50% by weight of polypropylene. The juniper wasprocessed with a hammermill to approximately {fraction (1/32)} inch anddried to a moisture content of less than 1%. The panel comprised thefollowing target characteristics: length of approximately 46 inches;width of approximately 46 inches; thickness of approximately 0.25inches; specific gravity of approximately 1.15 and a total mass ofapproximately 9,970 grams. A press temperature of approximately 195° C.was used together with a press time of approximately 17 minutes and amaximum gauge pressure of approximately 1000 psi. A cooling time ofapproximately 15 minutes was used. The final panel had a mass ofapproximately 10,505 grams, a thickness of approximately 0.297 inches,and a specific gravity of approximately 1.02. Thus, the actualcharacteristics for specific gravity and thickness were withinapproximately 20% of the target characteristics.

Example 4

A three layer composite panel, or board, of the present invention wasmanufactured. The panel comprised approximately 50% by weight of Juniperand approximately 50% by weight of polypropylene. The juniper wasprocessed with a hammermill to approximately {fraction (1/32)} inch forpanel faces and to approximately ¼ inch for a panel core. The juniperparticles were dried to a moisture content of less than 1%. The facematerial was divided approximately evenly and positioned to form twofaces whereas the core material was substantially disposed between theface material. The panel comprised the following target characteristics:length of approximately 46 inches; width of approximately 46 inches;thickness of approximately 0.625 inches; specific gravity ofapproximately 0.95 and a total mass of approximately 20,592 grams. Apress temperature of approximately 195° C. was used together with apress time of approximately 23 minutes and a maximum gauge pressure ofapproximately 1000 psi. A cooling time of approximately 20 minutes wasused. The panel mass before application of the press was approximately20,592 grams. One breathing cycle was used. The final panel had a massof approximately 20,425 grams, a thickness of approximately 0.630inches, and a specific gravity of approximately 0.94. Thus, the actualcharacteristics for specific gravity and thickness were withinapproximately 2% of the target characteristics.

Example 5

Whole juniper trees were chipped and the chips were put in a hammermillwith an approximately ¼ inch screen purchased from Montgomery Wards.Next, the chips processed using the ¼ inch screen were re-ground usingan approximately {fraction (1/32)} inch screen that was placed in thehammermill. After this step, the ground chips were run through a dryerfor 24 hours until the exit air was approximately 2% in moisture (from astart of approximately 8%). The dried wood was then mixed with anapproximately equal weight of plastic and mixed for approximately 10minutes. Next, the wood/plastic mixture was processed into a compositeboard using the inventive press method. The press method used a metalframe having an approximately ⅝ inch thickness. This metal frame wasplaced on a ¼ inch metal caul plate. A “forming box” was placed insidethe metal frame. The forming box was marked with an approximately 1 inchborder and a red line every approximately half inch and a black lineapproximately every ¼ inch. The wood/plastic mixture was then placedinto the box and leveled accordingly using the black and red lines forguidance. The mixture was then compressed by hand to form a mat usingboards having dimensions of approximately 18 inches by 18 inches. Next,four square pressing boards were placed temporarily in each of the fourcomers to prevent the mat from falling apart in the comers while theforming box was removed. After removal of the forming box, the foursquare pressing boards were removed. Next, an approximately ¼ inch metalcaul plate was placed on top of the mat and the press was heated toapproximately 360° F. Once heated to temperature, the press was engagedand a pressure of approximately 320 pounds per square inch was appliedfor approximately 30 minutes. After approximately 30 minutes, the presswas allowed to cool for approximately 20 minutes, after which time, thecomposite board was removed from the press. Alternatively, the compositeboard is removed to another station for cooling thereby eliminating theneed to cool the press. This alternative facilitates throughput byeliminating the need for large temperature differential cycling of thepress and providing for relatively constant temperature operation.

Example 6

The press or extrusion methods of the present invention are used tomanufacture novel composite boards having thicknesses from approximately⅛ inch to approximately ⅝ inch. Whole juniper and/or pine trees are usedbut is not limited to whole trees. The trees are chipped in the fieldand then brought to the processing plant. At the processing plant, thechips are dried to a moisture content of approximately 5% or less. Thedried chips are then processed using a hammermill with an approximately{fraction (1/32)} inch screen. The wood is then mixed with anapproximately equal weight of plastic, such as, polypropylene. Themixture is then heated, either by press or extruder, to a temperature ofapproximately 360° F. The mixture is allowed to cool thereby forming awaterproof composite board that resists rotting and decay. Suchinventive composite boards are suitable for use as signs for federaland/or state agencies.

Example 7

As in Example 6, a composite board is manufactured using the pressmethod of the present invention. An approximately 5 foot by 5 foot pressis used to heat the wood/plastic mixture. Next, the wood/plastic heatedmixture is transferred to a second cooling press where the cooledmixture forms a composite board.

Tests of Inventive Composite Boards

Composite boards of the present invention were manufactured and tested.The test results show that the inventive thermoplastic/junipercomposites are cost-effective candidates to replace the plywoodsubstrate of signs, such as those used by the U.S. Forest Service. Theadvantages of the inventive composite materials are good moistureresistance, good edge nailing capability, competitive cost, and betterdurability, especially when exposed to porcupine populations, whichpresently eat a large number of the signs supplied.

Tests were performed to determine how much wood, particularly juniperwood, can be used as a component in juniper/thermoplastic compositematerials of the present invention. A variety of inventive compositematerials were subjected to a series of standard ASTM tests and theresults were compared to published values of competing wood compositepanel products.

The objectives of the series of tests were to determine:

1. bending strength and stiffness of the material;

2. nail and screw withdrawal capacity of the material;

3. thickness swell and linear expansion properties of the material;

4. moisture absorption properties of the material;

5. internal bond strength of the material; and

6. shear strength of the material.

In addition to the above listed tests, material was placed in the fieldto determine if porcupines will eat it.

Raw Material Description and Preparation

For purposes of the tests, wood comprised an approximately 20 footdiameter Juniper tree that included needles, branches, trunk, bark andlimbs. Some of the trunk and limbs were processed in the field bygrinding in a hammermill, the rest of the material was sent a processingfacility where it was processed as in the field (limbs and trunks,typically known as cord material, cut to about three foot lengths). Thismaterial was further processed as disclosed below.

Juniper Cord Material Preparation

The cord material was processed by three methods:

Method 1: The field material was chopped in a hammermill. It was thenflaked at Washington State University's (WSU) Wood Materials andEngineering Laboratory (WMEL) using a Pallmann rotary blade flaker.

Method 2: The material was chipped and then flaked at Washington StateUniversity's (WSU) Wood Materials and Engineering Laboratory (WMEL)using a chipper and a Pallmann rotary blade flaker.

Method 3: The material was ground through a ⅞″ screen using a Filonegrinder. It was then flaked at Washington State University's (WSU) WoodMaterials and Engineering Laboratory (WMEL) using a Pallmann rotaryblade flaker.

Plastic Geometry and Quantity

All of the formulations tested comprised low density polyethylene (LDPE)film mixed with juniper furnish material in an approximately 50 percentby weight LDPE film and an approximately 50 percent by weight juniperfurnish. The film was a nominal ¼ inch grind in the formulation. A sieveanalysis was conducted on the plastic material to determine the exactparticle size distribution and approximate average particle size. The 50percent plastic level was chosen because preliminary moisture responsetests indicated that this level would be required to make a superiorexterior board substrate.

Final Density

Target density for all samples in Test Series 1 was 50 pcf. All sampleswere pressed to stops in the consolidation press. Nominal thickness wasapproximately ½ inch.

Composite Formulations

The following board formulations were tested in this test series:

Board 1A: 50% juniper field grind (unsifted), approximately 0.015″ thickand 50% PE approximately ¼″ grind. Board 1B: 50% juniper field grind,approximately 0.015″ thick, sifted to remove approximately ¼″ minus, and50% PE approximately ¼″ grind. Board 2A: 50% juniper approximately ½″chips, approximately 0.015″ thick, sifted to remove fines, and 50% PEapproximately ¼″ grind. Board 2B: 25% juniper approximately ½″ chipsflaked to approximately 0.015″ thick, 25% juniper approximately ⅜″ grindchips flaked to approximately 0.015″, and 50% PE approximately 1/4″grind. All juniper material was sifted to remove the fines. Board 2C:15% juniper approximately ½″ chips flaked to approximately 0.015″; 20%juniper approximately ⅜″ chips flaked to approximately 0.015″, 15%juniper approximately ¼″ chips flaked to approximately 0.015″, and 50%PE approximately ¼″ grind. All juniper furnish was sifted to remove thefines. Board 3A: 16% juniper approximately ⅞″ Filone grind flaked toapproximately 0.015″ and sifted to isolate approximately ½″ chips, 34%juniper approximately ⅞″ Filone grind flaked to approximately 0.015″ andsifted to isolate approximately ⅜″ flakes, and 50% PE approximately ¼″grind.

Performance Test Equipment and Procedures

All of the samples were formed on a PRESSAIRE™ large format press(24″×54″) (Engineered Composites, Boise, Id.). Physical property testswere conducted at a research facility in Boise, Id. During the pressingprocess, the core temperature was recorded using a Type 3 thermocouplewhose signal was processed by a data acquisition board. Plenum airpressure was measured using an Omega P 303-015G5V electronic sensorsthat have their signals processed by the data acquisition hardware.Airflow was measured using an Omega FLR871 0-SC electronic air flowmeter. The set point for the heaters was approximately 420° F., theairflow was set at approximately 650 scfm, and the plenum pressure wasapproximately 8 psig. Platen closure rate was approximately ⅜″ perminute.

All weights were measured by an electronic scale accurate toapproximately 0.01 pounds. Bulk density was determined by placing theunconsolidated fluff mixture into a one cubic foot container andweighing it. All thickness measurements were made using a TritonMicrometer accurate to approximately 0.001 inches. Wood flake moisturecontent was measured using a CompuTrac Moisture Meter accurate toapproximately 0.1 percent.

Sieve analysis was done on a Tyler RX-86 sieve shaker. The Tyler meshnumbers reported herein correspond to the following sieve openings: #5is approximately 0.157 inch; #8 is approximately 0.0937 inch; #14 isapproximately 0.0469 inch; and #20 is approximately 0.0331 inch. Weightsfor the sieve analysis were measured on a Mettler balance accurate toapproximately 0.1 gram.

All structural tests were conducted on a Universal Test Machine using aBLH LP1O 10 k load cell and a BLH LCP1O digital readout recordingdevice. All deflections were measured using a dial indicator accurate toapproximately 0.001 inches. All tests performed followed the AmericanSociety for Testing and Materials (ASTM) D1037 test methods listedbelow:

Static Bending Test Reference: ASTM D1037 - Section 11-20 Number ofSamples 9 per each formulation: Sample Size: 1/2″ × 3″ × 13″ Span: 11″Nail Withdrawal Test Reference: ASTM D1037 - Section 47-53 Number ofSamples 5 per each formulation: Sample Size: 1/2″ × 3″ × 6″ WaterAbsorption and Thickness Swell Test Reference: ASTM D1037 - Section100-106 Number of Samples 4 per each formulation: Sample Size: 1/2″ × 6″× 6″ Linear Expansion Test Reference: ASTM D1037 - Section 107-110Exception: Substitute Section 104 for (24 hr immersion) Section 109 (90%relative humidity) Number of Samples 5 per each formulation: SampleSize: 1/2 ″ × 3″ × 12″ Internal Bond Test Reference: ASTM D1037 -Section 28-33 Number of Samples 5 per each formulation: Sample Size:1/2″ × 2″ × 2″ Edgewise Shear Test Reference: ASTM D1037 - Section136-142 Number of Samples 5 per each formulation: Sample Size: 1/2″ × 31/2″ × 10″

Sieve Analysis Results

The results of the sieve analysis for particle distribution andapproximate average particle size are shown in FIGS. 5 through 10. Theaverage particle size is not based on the total number of particles butrather it is based on the weight percentage of the material retained ineach sieve tray in relation to the total sieved material weight. Inpractice a sieve retains particles greater than its associated meshsize. Sieve results, as shown in FIGS. 5 through 10 are also amenable toanalysis by standard statistical measures. For example, it is known inthe art to calculate geometric mean diameter and geometric standarddeviation from sieve data. Therefore, the materials of the presentinvention are optionally characterizable by geometric mean diameter andgeometric standard deviation. In general, a geometric mean is given bythe nth root of the product of “n” observations. For example, thegeometric mean diameter of a sieve, or bin, is the square root of theproduct of lower and upper sieve size. A program to calculate geometricmean diameter and geometric standard deviation from sieving results canbe obtained from Dr. Tim Herrmann, Department of Grain Science, KansasState University, Manhattan, Kans. and is hereby incorporated byreference.

FIG. 5 is a plot of retained material versus sieve size for the wood andplastic blend of Board 1A. Board 1A was formed from plastic having aparticle size distribution comprising an average particle size ofbetween approximately 0.25 inch and approximately 0.157 inch and woodhaving a particle size distribution comprising an average size betweenapproximately 0.0937 inch and approximately 0.0469 inch. FIG. 6 is aplot of retained material versus sieve size for the wood and plasticblend of 1B. Board 1B was formed from plastic having a particle sizedistribution comprising an average size of between approximately 0.25inch and approximately 0.157 inch and wood having a particle sizedistribution comprising an average size between approximately 0.1570inch and approximately 0.0937 inch. FIG. 7 is a plot of retainedmaterial versus sieve size for the wood and plastic blend of 2A. Board2A was formed from plastic having a particle size distributioncomprising an average size of between approximately 0.25 inch andapproximately 0.157 inch and wood having a particle size distributioncomprising an average size between approximately 0.1570 inch andapproximately 0.0937 inch. FIG. 8 is a plot of retained material versussieve size for the wood and plastic blend of 2B. Board 2B was formedfrom plastic having a particle size distribution comprising an averagesize of between approximately 0.1570 inch and approximately 0.0937 inchand wood having a particle size distribution comprising an average sizebetween approximately 0.1570 inch and approximately 0.0469 inch. FIG. 9is a plot of retained material versus sieve size for the wood andplastic blend of 2C. Board 2C was formed from plastic having a particlesize distribution comprising an average size of between approximately0.25 inch and approximately 0.157 inch and wood having a particle sizedistribution comprising an average size between approximately 0.1570inch and approximately 0.0469 inch. FIG. 10 is a plot of retainedmaterial versus sieve size for the wood and plastic blend of 3A. Board3A was formed from plastic having a particle size distributioncomprising an average size of between approximately 0.25 inch andapproximately 0.157 inch and wood having a particle size distributioncomprising an average size between approximately 0.25 inch andapproximately 0.0469 inch.

According to the present invention, a particle size distribution is notlimited to, for example, a Gaussian distribution, and comprises modaland/or skewed distributions. An approximate average size is determinablefrom any type of particle size distribution.

Results of Performance Tests

The results of the experiments are represented in Table 1.

TABLE 1 Test data comparison between juniper furnish/thermoplasticcomposite boards Ave Nail Ave. Screw Ave. Pull- Pull- Ave. Ave. Ave.Ave. Ave. Ave. Ave Internal out out Edgewise Water Thickness LinearSample Density MOR MOE Bond (lbs/in) (lbs/in) Shear Absorption SwellExpansion Board (pcf) (psi) (ksi) (psi) 6d nail Drywall (psi) (%) (%)(%) 1A 49.2 1321 101  75 120 457 917 15.4 1.9 0.156 1B 47.2 2183 171  87145 522 985 12.9 4.8 0.266 2A 44.8 2024 165 152 108 484 831 13.3 4.60.185 2B 45.8 2082 135 184 142 503 1073  12.5 2.4 0.293 2C 46.7 2225 165103 147 493 782 14.3 4.0 0.066 3A 48.8 2568 185  99 148 565 1060  15.13.2 0.122

Weatherometer Tests

Table 2 summarizes the results of weatherometer testing of agriculturalfibers combined with thermoplastic. The ultra-violet light exposure wasapproximately 1000 hours combined with cyclic moisture conditions; it issuppose to simulate between approximately 3 and approximately 5 years ofenvironmental exposure.

All of the samples tested that survived the 1000 hour exposuredemonstrated thickness swell increases in the 0.1%-6% range. The fivesamples that did not last that long tended to show signs of largeamounts of surface fiber pop, discoloration, some delamination, andrelatively large thickness swell (10-20%). The thermoplastic/cellulosesamples tested intentionally had a large proportion of them formulatedwith PVC siding material or PVC wire stripping material. This was donebecause PVC thermoplastic is known to have very good ultraviolet lightresistance. The investigators felt that by using this plastic we wouldbe able to better discern the effect of changes in fiber geometry,species, and etc. In retrospect this was a mistake because PVC also hasone of the highest melting points of the thermoplastics tested.Inspections made after the exposure using a stereoscope revealed thatthese PVC composites did not achieve full liquefaction at the time ofcomposite manufacture. Consequently, the results of the PVC formulationsare somewhat misleading, because complete bonding of the wood andplastic did not occur before the samples were exposed to the elements.

As mentioned supra, these tests demonstrate that composites made withpolyethylene as the thermoplastic binder perform very well in spite ofthe fact that this plastic has very low ultraviolet resistance. Theseresults demonstrate that the inventive composites are suited forapplications where UV exposure is a concern.

The following ratings were used to judge the various samples:

Discolor:

1—complete discoloration of the wood

2—no noticeable discoloration

Surface Pop:

5—no noticeable surface pop of the cellulose fibers

4—very slight release of surface fibers

3—release of about 40% of the surface fibers

2—release of more than 40% of the surface fibers

1—substantial release of surface fibers, delamination and/or less than1000 hours of exposure.

Swell %:

Calculated thickness swell based on average of four readings before andafter exposure. The swell % rating is only used to rank the samples inthe subject grouping.

TABLE 2 Weather Test Results. Color/ Surface/ Swell %/ Overall NumberPlastic Wood Rating Rating Rating Rating 27 50% PE {fraction (3/16)}″Grind Filone 1 4 0.8%/6 11 Juniper 28 50% PE Hammermill 1 4 0.6%/7 12Chipper Sagebrush 29 50% PE 50% Pine Sawdust 1   3.5 1.3%/5 9.5 49 48%HDPE, 2% 50% ¼″ Grind 1 3 2.9%/4 8 Coupling Agent Sifted Peanut Hulls 5148.5% PVC Wire ⅜″ Filone Grind 1 1 21%/1 3 Stripping Material, WheatStraw (741 1.5% Coupling agent hrs.) 52 48.5% PVC wire ¼″ Grind Almond 1  2.5 6.2%/3 6.5 stripping material, Shells 1.5% Coupling Agent 53 48.5%PVC wire 33% Rolled Full 1 1 9.0%/2 4 stripping material, Peanut Hulls;(500 1.5% Coupling Agent 15.5%, 0.015″ hrs.) Thick, 1″ long Filone grindDF

The agricultural furnishes performance were mixed. The samples withjuniper and sagebrush performed very well; the samples with peanutshells, almond hulls, and straw were uneven. It is unclear whether theuse of PVC that did not achieve full liquefaction and thus created poorbonding was the major cause of this uneven performance, or whether itwas due to the fiber itself. It did appear that the straw, peanutshells, and almond hulls did break down and turn white where they wereintensely exposed to the UV radiation.

The fibers that were encapsulated in polyethylene performed much betterthan those in PVC. Both the sagebrush and the juniper sample appeared asthough nothing had happened to them. The peanut hull sample with HDPEfilm as the plastic performed reasonably well, but the peanut hullsample with PVC plastic fell apart. It appears that the peanut andalmond hulls do tend to breakdown in UV exposure faster than wood. Thestraw sample did very poorly; this is probably due to the low resistanceof the fiber to UV exposure and the fact that the PVC plastic did notcompletely melt at the time of manufacture.

Close examination of the samples reveals that putting any kind ofcoating on the surface of the thermoplastic cellulose composite helpsprotect the material from UV degradation. All of the painted samples,stained samples, and paper coated samples performed exceptionally well.At first glance it appeared that Samples #30 and 32, which were bothcoated with latex, did experience some surface pop. However; on closerexamination of the control samples that were unexposed, it appeared thatthe surface pop appeared at the time the paint was applied rather thanafter exposure as was first assumed. Sample #33 had brown plastic coatedlumber wrap facing that bleached completely white, but it stillmaintained its integrity. There was no detectable surface delaminationwith the paper facing of this sample or Sample #34; this indicates thatthe plastic welding employed to attach the paper to thethermoplastic/wood composite works very well.

The results indicate that use of coupling agents in the matrix improvesthickness swell, and resistance to UV exposure. The coupling agentsamples had some of the lowest moisture swell numbers and their surfacepop resistance was also very good. The treated samples and thereformulated railroad ties also performed extremely well. It should benoted that both of these groupings used polyethylene as the matrixplastic. This plastic achieved a high degree of liquefaction when thecomposite was formed, and consequently it coated the fibers morecompletely than the PVC samples that were tested.

Mechanical Property Comparison With Other Materials

FIGS. 11-18 give a graphical picture of where Juniperfurnish/polyethylene thermoplastic composites are positioned relative toother materials. One new group was created, group 3A, which shows theprojected benefit to group 3A when a coupling agent is added; this groupis only shown in FIGS. 11 and 12. The data shown in these tables isactual test data taken from tests with identical procedures to thosereported here. The materials are off-the-self competing materials. Thereader should note that the OSB and Masonite specimens were commercialsiding products that are specially produced for this market.Consequently the numbers shown for these materials represent the bestperformance that can be expected for these classes of materials in anexterior environment. Edgewise shear measures the force required toshear the material. It's very important in highly loaded short spanloading conditions.

Conclusions of Test Results

The data presented in Table 1 indicate that all of the compositeformulations tested except Formulation IA would make acceptable materialfor sign applications. The data in Table 1 related to moisture responsedemonstrate the superior properties of the composites of the presentinvention. Data presented in FIGS. 17 and 18 indicate that thesejuniper/polyethylene thermoplastic composites have very competitivelinear expansion and thickness swell numbers. Good moisture stabilitynumbers indicate that the inventive composite materials exhibit verylittle movement when subjected to varying moisture conditions; thismeans that the application of thin overlays to this class of substrateare not likely to exhibit de-lamination or cracking.

The data presented in Table 2 indicate that the inventive compositematerials weather very well. The samples that were placed in theweatherometer showed almost no degradation. Tests on similarpolyethylene thermoplastic wood composites which subjected them to themuch harsher environment of a Termatron (soak, −40F., and +140F. cycles)have shown that these materials perform, in many regards, better thancurrently available wood composites.

The strength and stiffness data for the composites of the presentinvention are good; they exceed the particle board and hardboard sidingstandard of 1800 psi modulus of rupture. Data presented in FIGS. 11 and12 indicate that these materials are on the low end in terms of strengthand stiffness when compared with competing materials. Typically themodulus of elasticity (MOE), which is a measure of stiffness, is in therange of 250-350 psi for composite board materials. The juniperpolyethylene composites performed below those values. The presentinvention also encompasses the addition of coupling agent, whichincrease the bond between the juniper and the plastic. The use ofcoupling agents can increase stiffness and strength about 30%. However,an alternative to coupling agents, that provides additional benefits,results from decreasing the particle size of the wood and plastic.Stiffness (or rigidity) is important if the product you're competingagainst is a panel of equal thickness.

The internal bond numbers and the nail withdrawal data (FIGS. 13 and 14)show that the composite materials of the present invention holdfasteners very well. The relatively high internal bond numbers are anindication that edge splitting from nails driven close the edge will beminimal; this has been shown in actual test experience with thesematerials. The data presented in Table I indicate that the inventivecomposites also hold screws well. Heating and partial melting of plasticduring insertion followed by cooling and solidification is a possiblemechanism for nail and screw performance. The effect of frictional heatis that the plastic tends to mold itself around the nail, which tends toincrease holding power.

FIG. 5 shows data from the sieve analysis of formulation 1A and revealsthat this mix had a very high percentage of fines relative to theplastic particles. This is probably why its strength and stiffnessperformance was less than the other formulations. High percentages offurnish fines relative to the percentage of plastic tends to producenon-homogeneous boards with areas of clumped fines that have very lowamounts of binder. The result is a weak spot in the board. The data fromthis test series suggests that the juniper furnish will have to undergofurther processing to make an acceptable product for sign applications.Again, a decrease in the particle size of the wood and plastic overcamethese limitations and produced a superior product. For example, ahammermill was used to produce a final particle size of approximately0.03125 inch starting from whole one-seed juniper trees.

Tests show that this class of materials has very good impact resistanceand recovery when polyethylene type plastics are used.

Uniformity of particle size is achievable by sifting the material and/orgrinding to a particle size wherein fines are not substantially smallerthan the desired grind size. For example, a {fraction (1/32)} inchhammermill achieves particles comprising an average size closer to finesthan does a ¼ inch hammermill. According to the present invention,sifting is optionally performed on material to achieve a more uniformsize distribution.

Regardless of the particle size, according to the present invention,calculations are used to determine the amount of wood and plastic thatare needed to form a final product. In general, the starting wood andplastic densities are known as is the density of a starting mixture ofwood and plastic. Of course, the density of the mixture includes voidsbetween wood and/or plastic particles. For given dimensions of a finalproduct, a final product volume is calculated. An estimate of finalproduct density is obtained from the wood and plastic densities and therelative fraction of wood and plastic. Next, a final product weight isdetermined using the estimated final product density. Using the finalproduct weight, an equal weight of wood and plastic mixture is prepared.For the press method, this weight of wood and plastic forms the mat,whereas for the extrusion method, mass/weight flow rates are involved.The final product is checked against the originally specified dimensionsand a correction factor is determined if needed. Accordingly, the weightof the wood and plastic feed is adjusted. Alternatively, a final productdensity is determined and used instead of a final product estimateddensity. Again, most importantly, the final product is checked againstinitial specifications to ensure quality.

In the aforementioned examples (Boards 1A, 1B, 2A, 2B, 2C, and 3A) theparticle size distribution of the wood and plastic generally comprisesan average size between approximately 0.0469 inch and approximately 0.25inch. In a preferred embodiment of the present invention the particlesize distribution of the wood and plastic comprises an average size lessthan approximately 0.0937 inch and more preferably an average size ofless than approximately 0.0331 inch. For example, use of a hammermillwith a screen size of {fraction (1/32)} inch (0.03125 inch) results inwood and/or plastic particles comprising an average size less thanapproximately 0.0331 inch. As mentioned above, particles from ahammermill often comprise a dimension greater than the size of thehammermill screen (refer to FIGS. 1a and 1 b); however, at least onedimension of a particle will be less than or equal to that of a screenopening in order for the particle to pass through the screen. Thus,where the size of a particle is mentioned, it refers to a particlecomprising at least one dimension of that size. Where an averageparticle size is mentioned, this refers to particles comprising at leastone dimension of that size. Again, this description is sufficient forone of ordinary skill in the art of particle and/or sieve analysis tounderstand and appreciate.

The aforementioned adjustments to average particle size and/or particlesize distribution have improved the overall quality of the compositeproduct and eliminated many shortcomings associated with theaforementioned larger particle size products. In particular, the surfacecharacteristics are greatly improved. The smaller particle size materialalso facilitates use of extrusion methods as described supra.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverin the appended claims all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above are hereby incorporated by reference.

What is claimed is:
 1. A press method of making a composite materialcomprising the steps of: a) selecting a tree from the group consistingof conifers and junipers; b) preparing a natural material by grindingthe whole tree into particles having an average particle size of lessthan approximately 0.25 inch, the particles including trunk particles,branch particles, needle particles, and bark particles; c) providing aframe; d) loading the natural material and a plastic into the frame; ande) applying heat and pressure to the natural material and plastic in theframe.
 2. The press method of claim 1, further comprising the step ofremoving the composite material from the frame after the applying step.3. The press method of claim 1, further comprising the step of insertinga forming box into the frame.
 4. The press method of claim 1, furthercomprising the step of adjusting the packing of the natural material andplastic before the applying step.
 5. The press method of claim 1,wherein the applying step comprises applying heat to reach a temperatureof approximately 400° F.
 6. The press method of claim 1, wherein theapplying step comprises applying a pressure of approximately 8 psig. 7.The press method of claim 1, wherein grinding comprises a first grindingstep of grinding the whole tree to a maximum particle dimension of lessthan approximately 12 inches.
 8. The press method of claim 7, whereingrinding further comprises a second grinding step wherein the whole treeis ground to a maximum particle size of less than approximately 0.25inches.
 9. The press method of claim 8, further comprising a washingstep before the second grinding step.
 10. The press method of claim 9,further comprising a drying step before the second grinding step. 11.The press method of claim 8, further comprising screening the groundtree after the first grinding step and before the second grinding step.12. The press method of claim 8, further comprising a flaking stepbefore the second grinding step.
 13. The press method of claim 8,further comprising a sifting step after the second grinding step.
 14. Anextrusion method of making composite material comprising the steps of:a) selecting a tree from the group consisting of conifers and junipers;b) preparing a natural material by grinding the whole tree intoparticles having an average particle size of less than approximately0.25 inch, the particles including trunk particles, branch particles,needle particles, and bark particles; c) feeding the natural materialand a plastic into an extruder; d heating the natural material andplastic in the extruder; and e) extruding composite material comprisingthe natural material and plastic from the extruder.
 15. The extrusionmethod of claim 14, wherein the extruding step comprises extrudingcomposite material onto a film.
 16. The extrusion method of claim 14,further comprising the step of rolling extruded composite materialbetween two rollers.
 17. The extrusion method of claim 14, furthercomprising the step of cooling extruded material.
 18. The extrusionmethod of claim 14, wherein grinding comprises a first grinding step ofgrinding the whole tree to a maximum particle dimension of less thanapproximately 12 inches.
 19. The extrusion method of claim 18, whereingrinding further comprises a second grinding step wherein the whole treeis ground to a maximum particle size of less than approximately 0.25inches.
 20. The extrusion method of claim 19, further comprising awashing step before the second grinding step.
 21. The extrusion methodof claim 19, further comprising a drying step before the second grindingstep.
 22. The extrusion method of claim 19, further comprising screeningthe ground tree after the first grinding step and before the grindingstep.
 23. The extrusion method of claim 19 further comprising a flakingstep before the second grinding step.
 24. The extrusion method of claim19 further comprising a sifting step after the second grinding step.